Organic tertiary polyphosphine monooxides are useful as phosphorus ligands for transition metals in the formation of transition metal complexes for use as homogeneous catalysts in various carbonylation, hydrogenation, hydroformylation, homologation, and other reactions. Such uses have been reported by R. W. Wegman, et al., Chem. Soc., Chem. Commun., 1987, 1891, and in U.S. Pat. Nos. 4,400,548 and 4,670,570.
The direct oxidation of tertiary polyphosphines using oxidants like hydrogen peroxide, aqueous bromine, organic peroxides, oxygen, and the like leads to non-selective reactions, resulting in the formation of complex mixes comprising the unchanged starting material, and its monooxidized, dioxidized, etc. derivatives which are formed in statistically expected admixtures. S. L. Brock and J. M. Mayer, Inorg. Chem. 1991, 30, 2138 report a 13% yield of the desired monooxide by the direct oxidation.
U.S. Pat. No. 4,429,161 discloses a two-step process for the preparation of tertiary polyphosphine monooxides. The process is described as highly selective and said to yield, potentially, a very pure product. The process involves the selective monoalkylation of a tertiary polyphosphine to a monophosphonium salt, followed by isolation, recovery and, optionally, purification of this intermediate and the subsequent alkaline hydrolysis of the monophosphonium salt to the polyphosphine monooxide.
S. J. Berners-Price et al., Inorg. Chem. 1987, 26, 3383, report the in situ formation of the monooxide derivative of 1,2-bis(diphenylphosphino)ethane by reaction of 1,2-bis(diphenylphosphino)ethane with a stoichiometric amount of copper(II) sulfate. The compound was observed and characterized spectroscopically but was not isolated.
M. R. Mason and J. G. Verkade, Organometallics 1992, 11, 2212, report the formation of a series of bis phosphine monooxides by the stoichiometric oxidation of the corresponding bis phosphines by palladium(II) chloride or platinum(II) chloride. F. Ozawa et al., Chem. Lett. 1992, 2177, report similar stoichiometric oxidation of a fully aromatic bis phosphine.
The process of the present invention concerns a one-step catalytic method for the selective monooxidation of organic tertiary polyphosphines.